Interpretive Summary: Zinc deficiency increases the risk of developing infectious disease, including diarrheal disease, probably by impairing immune function. Thus zinc supplementation of infants, and perhaps pregnant women, is a potential way to decrease morbidity in infants. This paper reports the results of zinc supplementation on immune function of zinc-deficient and zinc-replete infant rats. The study showed that supplementation of pregnant rats with normal zinc status with additional zinc supplements during pregnancy had suppressive effects on cellular immune function in the intestinal tract for the offspring. These effects occurred when offspring were exposed to excess zinc during pregnancy and during lactation. This finding highlights the necessity of knowing the zinc status of subjects before zinc supplementation is recommended in order to prevent potential adverse effects.